We must start providing online help to support multiple
languages.
English, Arabic, French, and Chinese.
We use RoboHelp x5 today and many HelpIDs are manually
assigned.

Initial questions about using RH7 to manage multi-languages:
1. What is the best way to get my English RHP project from
RH5 into RH7?
Simply open it inRH7 or Import into an \english folder within
the RHP.

2. When taking the English RHP that uses HelpIDs and
maintaining it to now support other languages, what is the best way
to handle the context-sensitive issue.
--Can I use the same English help topic HelpIDs within the
Arabic, Chinese, French (as long as the Arabic/Ch/Fr help topics
match).

Let me start by saying that we am still (just about)
producing just single language documentation so very much
SingleEngineByPlane

For your first question, I'd say it would be best to maintain
separate RH projects for each language. However this would depend
on the size and complexity of the project. You could use
conditional build tags inside a single RH project but this could
get a little unwieldy on larger projects.

For your second question, if you maintained separate
projects, you could just copy the mapids between projects as the
topics would be the same content in the same folder structure -
just the language would be different. The mapids are just a marker
against the topic and are not affected by language settings.

I'd suggest downloading the RH7 trial and testing out the
above before making any firmer decision. You'd just need a couple
of projects (e.g. English and French) with a few topics with
mapids.